U.S. patent application number 14/187309 was filed with the patent office on 2014-08-28 for device for marine seismic explorations for deposits.
The applicant listed for this patent is Stephen Chelminski. Invention is credited to Stephen Chelminski.
Application Number | 20140238772 14/187309 |
Document ID | / |
Family ID | 51387009 |
Filed Date | 2014-08-28 |
United States Patent
Application |
20140238772 |
Kind Code |
A1 |
Chelminski; Stephen |
August 28, 2014 |
DEVICE FOR MARINE SEISMIC EXPLORATIONS FOR DEPOSITS
Abstract
An air gun for use in generating seismic energy impulses
operable at pressures below 1000 psi that reduces high frequencies
and cavitation around the discharge of the air gun in order to
mitigate damage to the marine environment, the air gun providing a
sliding seal at the firing piston, an extension of port widths
beyond the diameter of the firing piston and capability to control
the speed of the shuttle assembly to reduce and eliminate some of
the possible causes of the objectionable high frequencies and
cavitation.
Inventors: |
Chelminski; Stephen;
(Antrim, NH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Chelminski; Stephen |
Antrim |
NH |
US |
|
|
Family ID: |
51387009 |
Appl. No.: |
14/187309 |
Filed: |
February 23, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61768496 |
Feb 24, 2013 |
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61791342 |
Mar 15, 2013 |
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Current U.S.
Class: |
181/119 |
Current CPC
Class: |
G01V 1/137 20130101;
G01V 1/38 20130101 |
Class at
Publication: |
181/119 |
International
Class: |
G01V 1/137 20060101
G01V001/137 |
Claims
1. An air gun for seismic exploration, comprising: a cylindrical
housing having a plurality of discharge ports; a bulkhead wall
within the cylindrical housing to separate an operating chamber
from an air cushion chamber; a shuttle assembly having a shaft
inserted through a central opening in the bulkhead wall and having
an operating flange on an end of the shaft within the operating
chamber; a cup shaped firing piston secured to an opposing end of
the shuttle assembly shaft, the firing piston separating the air
cushion chamber from the firing chamber; and wherein the air
cushion chamber is of a length along the shuttle axis that is at
least 1.2 times the length of the operating chamber along the
shuttle axis.
2. The air gun for seismic exploration of claim 1 wherein the air
gun operates at pressures below 1000 psi and more preferably within
a range of 400 psi to 600 psi.
3. The air gun for seismic exploration of claim 1 wherein the
bulkhead wall is vacuum brazed within the cylindrical housing.
4. The air gun for seismic exploration of claim 1 wherein the
central opening in the bulkhead wall having shaft seal rings and a
retainer ring.
5. The air gun for seismic exploration of claim 1 wherein the
shuttle assembly shaft having a hollow bore through the shaft and
cylindrical bearings and piston rings within the hollow bore of the
shuttle assembly shaft.
6. The air gun for seismic exploration of claim 5 further
comprising a shuttle assembly support spindle inserted within the
hollow bore.
7. The air gun for seismic exploration of claim 1 further
comprising snap rings to attach the firing chamber and an operating
chamber head to the cylindrical housing.
8. The air gun for seismic exploration of claim 1 further
comprising a backbone vacuum brazed permanently in place on top of
and to reinforce the cylindrical housing and serve as a flat
mounting surface for solenoid operated air gun firing valve.
9. The air gun for seismic exploration of claim 8 further
comprising a trigger air passage directly through the backbone and
the bulkhead wall to an annular space of the operating flange
within the operating chamber.
10. The air gun for seismic exploration of claim 8 further
comprising a solenoid valve housing detachable from the reinforcing
backbone, the solenoid valve housing enclosing one of at least a
solenoid operated air gun firing valve and a firing circuit.
11. The air gun for seismic exploration of claim 8 further
comprising a solenoid valve housing vacuum brazed to the
reinforcing backbone, the solenoid valve housing enclosing one of
at least a solenoid operated air gun firing valve and a firing
circuit.
12. The air gun for seismic exploration of claim 1 wherein the cup
shaped firing piston having a sliding seal preventing air leaks
between the cylindrical housing, firing chamber and air cushion
chamber until the air gun is triggered and air is released through
the plurality of discharge ports.
13. The air gun for seismic exploration of claim 1 wherein the
plurality of discharge ports having at least one horizontal post
divider and the ports extending beyond the outer diameter of the
cup shaped firing piston, said ports pointing outwardly opposite
each other and horizontally away from the center line of the air
gun.
14. A low pressure air gun for seismic exploration which reduces
spurious high frequency sounds, comprising: a cylindrical housing;
a bulkhead wall within the cylindrical housing to separate an
operating chamber from an air cushion chamber; a central opening in
the bulkhead wall; a shuttle assembly having a shaft inserted
through the central opening in the bulkhead wall and having an
operating flange on an end of the shaft within the operating
chamber; a cup shaped firing piston secured to an opposing end of
the shuttle assembly shaft separating the air cushion chamber from
the firing chamber; a plurality of ports formed within the
cylindrical housing, the width of the ports extending to a distance
greater than the outer diameter of the cup shaped firing piston; a
firing chamber secured to the cylindrical housing; and wherein the
air gun operates at pressures is in a range of 400 psi to 1000
psi.
15. The low pressure air gun for seismic exploration which reduces
spurious high frequency sounds of claim 14, wherein the air cushion
chamber in a set position is of a length along the shuttle axis
that is at least 1.2 times the length within the operating chamber
along the shuttle axis as measured from the face of the operating
flange to an operating chamber head.
16. The low pressure air gun for seismic exploration which reduces
spurious high frequency sounds of claim 14 further comprising a
speed controller, the speed controller comprising: a fluted sleeve
installed within the operating chamber; a piston ring installed to
the outer diameter of the operating flange; and when triggered the
operating flange moves the piston ring over the fluted sleeve to
control the speed of the shuttle assembly.
17. The low pressure air gun for seismic exploration which reduces
spurious high frequency sounds of claim 16 wherein the speed
controller controls the speed of the shuttle assembly to control
the rise time from zero pressure to peak pressure of the primary
pressure pulse.
18. The low pressure air gun for seismic exploration which reduces
spurious high frequency sounds of claim 16 wherein the speed
controller fluted sleeve having grooves and the slope of the rise
time of the primary pressure pulse is adjusted by modifying the
geometry of one of at least the length, width, depth, slope and
shape of the grooves.
19. The low pressure air gun for seismic exploration which reduces
spurious high frequency sounds of claim 14 further comprising a
fluid filled speed controller.
20. The low pressure air gun for seismic exploration which reduces
spurious high frequency sounds of claim 15 further comprising snap
rings to attach the firing chamber and the operating chamber head
to the cylindrical housing.
21. The low pressure air gun for seismic exploration which reduces
spurious high frequency sounds of claim 14 further comprising a
backbone vacuum brazed permanently in place on top of and to
reinforce the cylindrical housing and serve as a flat mounting
surface for solenoid operated air gun firing valve.
22. The low pressure air gun for seismic exploration which reduces
spurious high frequency sounds of claim 21 further comprising a
trigger air passage directly through the backbone and the bulkhead
wall to an annular space of the operating flange within the
operating chamber said trigger air passage length less than radius
of the operating flange.
23. The low pressure air gun for seismic exploration which reduces
spurious high frequency sounds of claim 21 further comprising a
solenoid valve housing detachable from the reinforcing backbone,
the solenoid valve housing enclosing one of at least a solenoid
operated air gun firing valve and a firing circuit.
24. The low pressure air gun for seismic exploration which reduces
spurious high frequency sounds of claim 21 further comprising a
solenoid valve housing vacuum brazed to the reinforcing backbone,
the solenoid valve housing enclosing one of at least a solenoid
operated air gun firing valve and a firing circuit.
25. The low pressure air gun for seismic exploration which reduces
spurious high frequency sounds of claim 14 wherein the bulkhead
wall is brazed in place to the cylindrical housing.
26. The low pressure air gun for seismic exploration which reduces
spurious high frequency sounds of claim 14 further comprising shaft
seal rings and a retainer ring installed within the central opening
in the bulkhead wall around the shuttle assembly shaft to seal the
operating chamber from the air cushion chamber.
27. The low pressure air gun for seismic exploration which reduces
spurious high frequency sounds of claim 14 wherein the cup shaped
firing piston having a sliding seal preventing air leaks between
the cylindrical housing, firing chamber and air cushion chamber
until the air gun is triggered and air is released through the
plurality of ports.
28. The low pressure air gun for seismic exploration which reduces
spurious high frequency sounds of claim 14 wherein the plurality of
ports having at least one horizontal post divider and the ports
extending beyond the outer diameter of the cup shaped firing
piston, said ports pointing outwardly opposite each other and
horizontally away from the center line of the air gun.
29. A method of reducing spurious high frequency sounds from an air
gun, comprising the steps of: assembling an air gun having a
cylindrical housing; vacuum brazing a bulkhead wall within the
cylindrical housing to separate an operating chamber from an air
cushion chamber; installing close fitting shaft seal rings and a
retainer ring within a central opening in the bulkhead wall;
inserting a shuttle assembly having a shaft through the central
opening in the bulkhead wall to seal the operating chamber from the
air cushion chamber, the shuttle assembly shaft having a hollow
bore through the shaft and having an operating flange on an end of
the shaft within the operating chamber; inserting a fluted sleeve
within the operating chamber; installing a piston ring to the outer
diameter of the operating flange; installing cylindrical bearings
and shaft seal rings within the hollow bore of the shuttle assembly
shaft; inserting a shuttle assembly support spindle within the
hollow bore; affixing an operating chamber head to the cylindrical
housing snap rings; affixing a cup shaped firing piston to an
opposing end of the shuttle assembly shaft within the air cushion
chamber; forming a plurality of ports within the cylindrical
housing, the width of the ports extending to a distance greater
than the outer diameter of the cup shaped firing piston; affixing a
firing chamber to the cylindrical housing snap rings; supplying an
air trigger pulse to the operating flange to move the piston ring
over the fluted sleeve to control the speed of the operating flange
and thereby the rise time from zero pressure to peak pressure of
the primary pressure pulse as air is expelling from the ports as
the bottom end of the cup shaped firing piston crosses an edge of
the plurality of ports.
30. The method of reducing spurious high frequency sounds from an
air gun of claim 29, further comprising the steps of: vacuum
brazing a reinforcing backbone to the cylindrical housing; and
vacuum brazing a solenoid valve housing to the reinforcing
backbone, the solenoid valve housing enclosing a solenoid operated
air gun firing valve and firing circuit.
31. The method of reducing spurious high frequency sounds from an
air gun of claim 29, further comprising the step of: sealing the
bottom end of the cup shaped firing piston to the firing chamber
using a spring loaded backup ring and sliding firing seal.
32. The method of reducing spurious high frequency sounds from an
air gun of claim 29 further comprising the step of operating the
air gun at pressures below 1000 psi and more preferably within a
range of 400 psi to 600 psi.
33. The method of reducing spurious high frequency sounds from an
air gun of claim 29 further comprising the step of assembling the
air cushion chamber in a set position to a length along the shuttle
axis that is at least 1.2 times the length within the operating
chamber along the shuttle axis as measured from the face of the
operating flange to an operating chamber head.
Description
RELATED PATENT APPLICATIONS
[0001] This application claims the benefit of pending U.S.
Provisional Patent Application No. 61/768,496 filed Feb. 24, 2013
and U.S. Provisional Patent Application No. 61/791,342 filed Mar.
15, 2013 both applications entitled DEVICE FOR MARINE SEISMIC
EXPLORATIONS FOR DEPOSITS which are each hereby incorporated herein
by reference in the entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to air guns intended for use
in generating seismic energy impulses, i.e. acoustical waves, in a
body of water. More particularly, this invention relates to low
pressure air guns operable at pressures below 1000 psi in order to
mitigate damage to the marine environment by reducing or
eliminating high frequency sounds which are thought to be the
source of damage to the hearing of marine mammals and fish as well
as disturbing the habitats and well-being of marine life.
BACKGROUND OF THE INVENTION
[0003] Air guns, as used herein, are sound sources for marine
seismic exploration for petroleum deposits. The operating
components of air guns of the prior art include a firing chamber
holding a charge of gas under high pressure, a two-piston shuttle
assembly having a firing piston which retains the charge of
pressurized gas within the firing chamber, and an operating piston
positioned within an operating chamber where highly pressurized gas
acts against the operating piston to maintain the shuttle assembly
in a closed position until firing. A hollow shaft of the shuttle
assembly interconnects the two pistons and provides for pressurized
gas to flow from the operating chamber through the shaft to charge
the firing chamber. The air gun is triggered using a solenoid
operated valve to release high pressure air into the operating
chamber actuating the shuttle assembly to cause an abrupt discharge
of high pressure air from the firing chamber through discharge
ports and directly into the surrounding water, the water in which
the air gun is immersed.
[0004] Air guns of the prior art are normally run using an air
compressor on board an exploration vessel that yields high pressure
compressed air in the range of 2000 psi to 3000 psi. The air gun is
towed astern. The return signals are received by an array of towed
hydrophones. Air guns are relatively deep penetration sources,
operating with output frequencies generally between 10 Hz to about
1200 Hz, to identify subsurface geologic layers and define the
subsurface structure. The present invention provides many
advantages considered significant and valuable by the inventor
hereof. The inventor hereof has additional patents such as U.S.
Pat. Nos. 3,379,273 4,038,630, 4,271,924, 4,599,712, 4,779,245,
5,432,757, and 8,223,591. There are also some other inventors in
the same field such as Fiske, U.S. Pat. No. 4,757,482, Mayzes, U.S.
Pat. No. 5,315,917, Jensen U.S. Pat. No. 7,269,099 and others in
the field.
OBJECTS AND SUMMARY OF THE INVENTION
[0005] As noted, air guns of the prior art that are used for oil
exploration typically use air pressures of from 2000 psi to 3000
psi which explodes from the air guns when they are triggered thus
producing the sound pulses used for seismic analysis. The high
operating pressures of these air guns produce spurious high
frequency sounds which are not helpful for the purpose of finding
oil and which are thought to be the source of damage to the hearing
of marine mammals and fish as well as disturbing the habitats and
well-being of marine life. There is recently mounting pressure on
the exploration industry to eliminate these high frequencies from
the pulses of the air gun arrays used. Possible causes of these
high frequencies being, 1) the high pressure which air guns are run
at cause cavitation at the corners of the ports as the air bursts
out of the ports; 2) high pressure air leaking from clearances
between the gun housing and shuttle as the shuttle accelerates
after being triggered before clearing the ports; 3) conventional
air guns shoot a slug of water out of the ports as the shuttle
accelerates after the gun is triggered this slug of water may be
producing a water gun effect causing cavitation as water guns do
when they are triggered; and 4) the high pressure air may rush out
of the ports at such high velocity as to cause high frequency
sounds due to cavitation around the edges of the ports during its
acceleration from the ports. The high pressures as well produce a
very short rise time of the initial pulse that is thought to also
be a cause of unwanted high frequencies. The air gun of the present
invention reduces high frequencies and cavitations by providing a
sliding seal at the firing piston, extending the discharge port
widths beyond the diameter of the firing piston and controlling the
speed of the shuttle assembly to control the rate of release of
pressurized air through the outlet ports. By controlling the rate
of release of the pressurized air, the rise time from zero pressure
to peak pressure of the first or primary pressure pulse may be
slowed, increasing the time to reach peak pressure which may in
fact reduce some of the causes the objectionable high frequencies
and cavitation. Additionally, providing an air gun which fires at
low pressure will itself be a source of reduced high frequency
noise.
[0006] It is an object of the present invention to operate an air
gun at low pressures below 1000 psi and more preferably at
pressures from 400 psi-600 psi.
[0007] It is another object of the invention to provide an air gun
which produces little or no harmful high frequencies.
[0008] It is another object of the invention to provide an air gun
which produces increased low frequency output.
[0009] It is another object of the invention to provide an air gun
which reduces cavitation around the air gun to limit the disruption
of the marine ecosystem.
[0010] It is another object of the invention to provide a sound
source which will produce more low frequency energy and less high
frequencies.
[0011] It is another object of the present invention to assemble an
air gun lighter in construction in proportion to the lower
operating pressure of a low pressure air gun as compared to the
operating pressure of a conventional high pressure air gun thereby
producing a lighter and more easily handled air gun.
[0012] It is another object of the present invention to assemble a
low pressure air gun using a snap ring to affix the firing chamber
to the cylindrical housing of the low pressure air gun housing.
[0013] It is another object of the present invention to assemble a
low pressure air gun using a snap ring to affix the operating
chamber head to the cylindrical housing of the low pressure air gun
housing.
[0014] It is another object of the present invention to reduce the
use of bolts or clamp rings in assembling the air gun by using snap
rings.
[0015] It is another object of the present invention to assemble a
low pressure air gun having shuttle assembly flanges that are
thinner and lighter than conventional high pressure air guns
providing for faster acceleration of the shuttle assembly within
the air gun housing.
[0016] It is another object of the present invention to assemble a
low pressure air gun having a sliding firing seal that is directly
adjacent to the ports to prevent the release of air from the firing
chamber until the firing piston moves past the ports.
[0017] It is another object of the present invention to prevent
leakage during the acceleration distance.
[0018] It is another object of the present invention to extend the
width of the ports beyond the outer diameter of the firing piston
providing a larger communication area of air expelled to the
outside water for the least amount of travel of the shuttle
assembly.
[0019] It is another object of the present invention to improve the
firing precision of the air gun by providing a shortened trigger
air passage, the air passage at a length shorter than the radius of
the operating flange.
[0020] It is another object of the invention to provide an air
cushion chamber of a length that is approximately 20% longer in
length than the length of the operating chamber thereby reducing
pressure buildup in the air cushion chamber that may decrease the
length of the stroke of the shuttle assembly.
[0021] It is another object of the invention to provide full
opening of the ports at low pressure.
[0022] It is another object of the invention that from a set
position the distance from the inner face of the firing piston is
longer than the distance from the face of the operating flange to
the chamber head.
[0023] It is another object of the invention to assemble an air gun
having a piston ring on the outside diameter of the shuttle
assembly operating flange.
[0024] It is another object of the invention to control the speed
of the shuttle assembly through adjustment of the geometry of
grooves by adjusting the depth, width, length, and slope of grooves
within a fluted sleeve within the operating chamber.
[0025] It is another object of the present invention to provide an
air gun with improved shuttle assembly speed control.
[0026] It is another object of the present invention to control the
rise time from zero pressure to peak pressure of the first or
primary pressure pulse to increase the time to reach peak pressure
to reduce or eliminate objectionable high frequencies.
[0027] It is another object of the present invention to assemble a
low pressure air gun using vacuum oven brazing at mating surfaces
to affix a reinforcing backbone to the cylindrical housing, the
back bone having air passages for providing compressed air to the
low pressure air gun.
[0028] It is another object of the present invention to assemble a
low pressure air gun using vacuum oven brazing to affix a bulkhead
wall within the cylindrical housing of the air gun.
[0029] It is another object of the present invention to reduce
degradation and wear on seals and structural components of the low
pressure air gun.
[0030] It is a still further object of the invention to provide an
air gun which by virtue of being operated at low pressures is
safer.
[0031] The present invention is related to an air gun for seismic
exploration, that comprises a cylindrical housing having a
plurality of discharge ports; a bulkhead wall within the
cylindrical housing to separate an operating chamber from an air
cushion chamber; a shuttle assembly having a shaft inserted through
a central opening in the bulkhead wall and having an operating
flange on an end of the shaft within the operating chamber; a cup
shaped firing piston secured to an opposing end of the shuttle
assembly shaft, the firing piston separating the air cushion
chamber from the firing chamber; and wherein the air cushion
chamber is of a length along the shuttle axis that is at least 1.2
times the length of the operating chamber along the shuttle
axis.
[0032] The air gun for seismic exploration operates at pressures
below 1000 psi and more preferably within a range of 400 psi to 600
psi. The bulkhead wall of the air gun for seismic exploration may
be vacuum brazed within the cylindrical housing. The central
opening in the bulkhead wall of the air gun may have shaft seal
rings and a retainer ring. The shuttle assembly shaft has a hollow
bore through the shaft and cylindrical bearings and piston rings
within the hollow bore and a shuttle assembly support spindle is
inserted within the hollow bore. The air gun for seismic
exploration further comprises snap rings to attach the firing
chamber and an operating chamber head to the cylindrical housing.
The air gun for seismic exploration further comprises a backbone
vacuum brazed permanently in place on top of and to reinforce the
cylindrical housing and serve as a flat mounting surface for
solenoid operated air gun firing valve. The air gun for seismic
exploration further comprises a trigger air passage directly
through the backbone and the bulkhead wall to an annular space of
the operating flange within the operating chamber. The air gun may
comprise a solenoid valve housing detachable from the reinforcing
backbone, the solenoid valve housing enclosing one of at least a
solenoid operated air gun firing valve and a firing circuit.
Alternatively, the air gun may comprise a solenoid valve housing
vacuum brazed to the reinforcing backbone. The cup shaped firing
piston of the air gun may have a sliding seal preventing air leaks
between the cylindrical housing, firing chamber and air cushion
chamber until the air gun is triggered and air is released through
the plurality of discharge ports. The plurality of discharge ports
of the air gun may have at least one horizontal post divider and
the ports may extend beyond the outer diameter of the cup shaped
firing piston, and the ports may point outwardly opposite each
other and horizontally away from the center line of the air
gun.
[0033] The present invention further relates to a low pressure air
gun for seismic exploration which reduces spurious high frequency
sounds, that comprises a cylindrical housing; a bulkhead wall
within the cylindrical housing to separate an operating chamber
from an air cushion chamber; a central opening in the bulkhead
wall; a shuttle assembly having a shaft inserted through the
central opening in the bulkhead wall and having an operating flange
on an end of the shaft within the operating chamber; a cup shaped
firing piston secured to an opposing end of the shuttle assembly
shaft separating the air cushion chamber from the firing chamber; a
plurality of ports formed within the cylindrical housing, the width
of the ports extending to a distance greater than the outer
diameter of the cup shaped firing piston; a firing chamber secured
to the cylindrical housing; and the air gun operates at pressures
is in a range of 400 psi to 1000 psi.
[0034] The air cushion chamber of the low pressure air gun for
seismic exploration which reduces spurious high frequency sounds
may be of a length along the shuttle axis that is at least 1.2
times the length within the operating chamber along the shuttle
axis as measured from the face of the operating flange to an
operating chamber head. The low pressure air gun for seismic
exploration which reduces spurious high frequency sounds may
further comprise a speed controller which comprises a fluted sleeve
installed within the operating chamber; a piston ring installed to
the outer diameter of the operating flange; and when triggered the
operating flange moves the piston ring over the fluted sleeve to
control the speed of the shuttle assembly. The speed controller
controls the speed of the shuttle assembly to control the rise time
from zero pressure to peak pressure of the primary pressure pulse.
The speed controller fluted sleeve has grooves and the slope of the
rise time of the primary pressure pulse is adjusted by modifying
the geometry of one of at least the length, width, depth, slope and
shape of the grooves. The low pressure air gun may further comprise
a fluid filled speed controller.
[0035] The low pressure air gun for seismic exploration which
reduces spurious high frequency sounds further comprises snap rings
to attach the firing chamber and the operating chamber head to the
cylindrical housing. The low pressure air gun for seismic
exploration which reduces spurious high frequency sounds further
comprises a backbone vacuum brazed permanently in place on top of
and to reinforce the cylindrical housing and serve as a flat
mounting surface for solenoid operated air gun firing valve. The
low pressure air gun further comprises a trigger air passage
directly through the backbone and the bulkhead wall to an annular
space of the operating flange within the operating chamber said
trigger air passage length less than radius of the operating
flange. The low pressure air gun may further comprise a solenoid
valve housing detachable from the reinforcing backbone, the
solenoid valve housing enclosing one of at least a solenoid
operated air gun firing valve and a firing circuit. Alternatively,
the low pressure air gun may further comprise a solenoid valve
housing vacuum brazed to the reinforcing backbone. The bulkhead
wall of the low pressure air gun may be brazed in place to the
cylindrical housing. The low pressure air gun may further comprise
shaft seal rings and a retainer ring installed within the central
opening in the bulkhead wall around the shuttle assembly shaft to
seal the operating chamber from the air cushion chamber. The cup
shaped firing piston of the low pressure air gun may have a sliding
seal preventing air leaks between the cylindrical housing, firing
chamber and air cushion chamber until the air gun is triggered and
air is released through the plurality of ports. The plurality of
ports of the low pressure air gun may have at least one horizontal
post divider and the ports may extend beyond the outer diameter of
the cup shaped firing piston, said ports pointing outwardly
opposite each other and horizontally away from the center line of
the air gun.
[0036] The present invention is further related to a method of
reducing spurious high frequency sounds from an air gun, comprising
the steps of assembling an air gun having a cylindrical housing;
vacuum brazing a bulkhead wall within the cylindrical housing to
separate an operating chamber from an air cushion chamber;
installing close fitting shaft seal rings and a retainer ring
within a central opening in the bulkhead wall; inserting a shuttle
assembly having a shaft through the central opening in the bulkhead
wall to seal the operating chamber from the air cushion chamber,
the shuttle assembly shaft having a hollow bore through the shaft
and having an operating flange on an end of the shaft within the
operating chamber; inserting a fluted sleeve within the operating
chamber; installing a piston ring to the outer diameter of the
operating flange; installing cylindrical bearings and shaft seal
rings within the hollow bore of the shuttle assembly shaft;
inserting a shuttle assembly support spindle within the hollow
bore; affixing an operating chamber head to the cylindrical housing
snap rings; affixing a cup shaped firing piston to an opposing end
of the shuttle assembly shaft within the air cushion chamber;
forming a plurality of ports within the cylindrical housing, the
width of the ports extending to a distance greater than the outer
diameter of the cup shaped firing piston; affixing a firing chamber
to the cylindrical housing snap rings; supplying an air trigger
pulse to the operating flange to move the piston ring over the
fluted sleeve to control the speed of the operating flange and
thereby the rise time from zero pressure to peak pressure of the
primary pressure pulse as air is expelling from the ports as the
bottom end of the cup shaped firing piston crosses an edge of the
plurality of ports. The method of reducing spurious high frequency
sounds from an air gun may further comprise the steps of vacuum
brazing a reinforcing backbone to the cylindrical housing; and
vacuum brazing a solenoid valve housing to the reinforcing
backbone, the solenoid valve housing enclosing a solenoid operated
air gun firing valve and firing circuit. The method of reducing
spurious high frequency sounds from an air gun may further comprise
the step of sealing the bottom end of the cup shaped firing piston
to the firing chamber using a spring loaded backup ring and sliding
firing seal. The method of reducing spurious high frequency sounds
from an air gun may further comprise the step of operating the air
gun at pressures below 1000 psi and more preferably within a range
of 400 psi to 600 psi.
[0037] These and other features, advantages and improvements
according to this invention will be better understood by reference
to the following detailed description and accompanying drawings.
While references may be made to upper, lower, vertical and
horizontal, these terms are used merely to describe the
relationship of components and not to limit the operation of the
present invention to any one orientation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] The invention, together with further objects, features,
aspects and advantages thereof will be more fully understood and
appreciated by consideration of the following description in
conjunction with the accompanying drawings in which the respective
elements bear the same reference numerals throughout the various
views.
[0039] FIG. 1 is a longitudinal cross sectional view of an
embodiment of the air gun of the present invention;
[0040] FIG. 2 is an end view of an embodiment of the air gun of the
present invention showing an electrical cable block connector that
may be optionally on the top or side of the solenoid valve housing
of the present invention;
[0041] FIG. 3 is a top view of an embodiment of the air gun of the
present invention;
[0042] FIG. 4A is a longitudinal cross sectional view of an
embodiment of the solenoid valve housing and operating chamber of
the air gun of the present invention;
[0043] FIG. 4B is a longitudinal cross sectional view of an
embodiment of the operating chamber of the air gun of the present
invention;
[0044] FIG. 5A is a longitudinal cross sectional view of an
embodiment of the liner sleeve of the operating chamber of the air
gun of the present invention;
[0045] FIG. 5B is a longitudinal cross sectional view of an
embodiment of the liner sleeve of the operating chamber of the air
gun of the present invention;
[0046] FIG. 5C is a cross sectional view along section A-A of FIG.
5A of an embodiment of the liner sleeve of the operating chamber of
the air gun of the present invention;
[0047] FIG. 6 is a longitudinal cross sectional view of a further
embodiment of the air gun of the present invention;
[0048] FIG. 7A is a longitudinal cross sectional view of an
embodiment of a fluid filled speed controller in the further
embodiment of the air gun of the present invention;
[0049] FIG. 7B is a cross sectional view along section A-A of FIG.
7A of an embodiment of a fluid filled speed controller in the
further embodiment of the air gun of the present invention;
[0050] FIG. 7C is a longitudinal cross sectional view of an
embodiment of a fluid filled speed controller in the firing
position in the further embodiment of the air gun of the present
invention;
[0051] FIG. 7D is a longitudinal cross sectional view of an
embodiment of a fluid filled speed controller in the set position
in the further embodiment of the air gun of the present
invention;
[0052] FIG. 8A is a longitudinal cross sectional view of an
embodiment of the firing chamber and discharge ports of the air gun
of the present invention;
[0053] FIG. 8B is a cut out cross sectional view of an embodiment
of the sliding firing seal and assembly of the air gun of the
present invention; and
[0054] FIG. 8C is a cross sectional view along section A-A of FIG.
8A of an embodiment of the firing chamber and discharge ports of
the air gun of the present invention.
DETAILED DESCRIPTION OF THE DRAWINGS
[0055] In an embodiment of the present invention, an air gun 10, as
shown in FIG. 1, comprises a dual purpose reinforcing backbone air
passage manifold 15 to strengthen the housing 18 to supply and
distribute compressed air through one or more passages 6 by
connecting a supply line to a connector 5 on either end of the
backbone 15. The backbone 15 may have one or more tow ears 8 that
may be brazed into the backbone 15 for towing the air gun 10. The
backbone 15 is secured to the air gun housing 18 by vacuum oven
brazing at mating surfaces 12 between the bottom of the backbone
and the air gun cylindrical housing providing a flattened top for
mounting a solenoid operated air gun firing valve eliminating the
necessity of using bolts to attach the backbone manifold 15 to the
housing 18, thus making the air gun more reliable and lighter.
Bulkhead wall 16 is also brazed into air gun housing 18 at joint 14
instead of the housing being machined out of a single billet of
stainless steel thus saving material costs, machine time, and
labor. The bulkhead wall 16 may be seated against a shoulder 9
formed in the housing 18 where the diameter of the housing 18 is
enlarged to secure the bulkhead wall 16 and form the tubular
structure of the operating chamber 30. Because the air gun 10 is
run at low pressures the housing 18 may have a dimensioned wall
thickness that is thinner than high pressure air guns of the prior
art, reducing the overall weight and costs of the air gun 10. The
shuttle assembly includes a shuttle assembly shaft 27 and an
operating flange 29. The shuttle assembly shaft 27 is inserted
through the opening to the operating chamber 30 and through a
center hole 11 in the bulkhead wall 16 with the sealing face of the
operating flange 29 aligning against the bulkhead wall 16. Instead
of using bolts or clamping rings, the operating chamber 30 is
enclosed by securing in place the operating chamber head 26 using a
retaining ring 28. The shuttle assembly support spindle 25 is
inserted into the hollow shuttle assembly shaft with and the
shuttle assembly support spindle flange 23 is secured to the
operating chamber head 26 using bolt circle 24. An air channel
block 22 is secured to the shuttle assembly support spindle flange
23 using bolt circle 21. The air channel block 22 has a 90.degree.
passage 4 to direct air flow through the air input fitting 19 and
through the spindle air passage 7 to inlet openings 31 to provide
air to the operating chamber 30. The compressed air input fitting
19 is secured to the backbone 15 using air input line retainer
bolts 33 to communicate with compressed air passage 6.
[0056] The shuttle assembly shaft 27 extends through the bulkhead
wall 16 to the air cushion chamber 50. The shaft 27 may be hollow
to reduce the overall weight of the air gun 10 and act as an air
supply passage for the air volume 60 within the firing chamber 62.
An air inlet orifice 51 controls the flow rate of air entering the
shaft interior bore 53 and an outlet orifice 55 controls the rate
of flow of air entering the volume 60 of the firing chamber 62. Air
is supplied from the operating chamber 30 through inlet holes 37 in
the shuttle assembly support spindle 25. The shaft end 48 of the
shuttle assembly shaft 27 is threaded and the cup shaped firing
piston 36 is attached to the shaft end 48 using a nut 57 to lock
the cup flange 36 against a shoulder 59 formed at the base of the
shaft 27. Rider bearings 179 installed along the outer diameter of
the cup shaped firing piston 36 to provide for the piston to freely
slide along the inner walls 20 of the low pressure air gun
cylindrical housing 18. In high pressure air guns of the prior art,
the space behind the firing piston is filled with water that is
displaced as the gun fires may cause cavitation that could disrupt
the marine ecosystem. By trapping ambient air behind the firing
piston, the displacement of water is reduced limiting a source of
cavitation around the water gun. A series of ports 70 are formed
through the housing 18 at the firing chamber 62 as indicated by
dotted lines 72 showing the openings. The firing chamber 62 may be
of any required dimension and may be replaced to adjust the size to
create a larger or smaller volume based on survey requirements. The
firing chamber 62 is secured to the air gun housing 18 using
retainer ring 38. By using snap type retainer rings instead of
bolts, the cylindrical walls of the housing 18 may be thinner where
there is no necessity to thicken the wall to install bolts or
clamping rings.
[0057] A solenoid valve housing 17 may be bolted using bolts 13 or
be brazed to the backbone 15. The solenoid valve housing 17 may
enclose only a solenoid valve 40 or a solenoid valve and control
circuit 42 based on the specification requirements of the air gun
system. An electrical cable block connector 80 extends either from
the top or side of the solenoid valve housing 17, as shown in FIG.
2. A multi-pin cable connector (not shown) provides for the cable
block connector 80 to be electrically connected to the solenoid
valve 40 or control circuit 42 components. The block connector 80
may then be bolted to the solenoid valve housing 17 using bolts 82.
The cable block connector 80 may be detached to replace the entire
solenoid valve housing 17 with the solenoid valve 40 and control
circuit 42 as a unit. Alternatively, an access cover 4 attached to
the solenoid valve housing 17 using bolts 3 may be provided to
provide access to repair or replace the solenoid valve housing 17
internal components. In this manner a defective control circuit or
solenoid valve can be repaired or replaced without removal of the
solenoid valve housing from the backbone 15. The cable block
connector 80 further provides for a faulty air gun 10 to be
replaced by only disconnecting the electrical cable block connector
80 from the solenoid valve housing and the air supply line from the
backbone 15 and attaching the cable block connector 80 and air
supply line to a new air gun 10, greatly reducing down time for
failures during deployment of an array of air guns. As shown the
trigger air passage 58 extends between the air passages 6 directly
through the backbone 15 to provide for more precise firing of the
air gun 10 where the air trigger passage is of a substantially
shortened length as compared to air guns of the prior art.
[0058] A top view of the air gun 10 is shown in FIG. 3 with the
electric cable block connector 80 directed off to the side of the
solenoid valve housing 17 and electrical cables 84 extending from
the block connector 80 to the exploration vessel or other similar
air guns. Air supply lines 86 extend from each end of the backbone
15. A second air passage 6 may be provided for additional air
supply lines if a number of air guns 10 are used in a single array.
The trigger air passage 58 directs air flow to a grooved annular
space 67 around the inner face of the operating flange 29 as shown
in FIG. 4A.
[0059] The present invention does not require holes to be drilled
through the bulkhead wall 16 to allow water to flow to lubricate
the shaft seals because the shuttle assembly shaft 27 is sealed
using two close fitting self-lubricating shaft seal rings 32, as
shown in FIG. 4B, that seal the operating chamber 30 from the air
cushion chamber 50 and allow the shuttle shaft 27 to move freely
through the center hole 11 of the bulkhead wall 16 without leakage.
A retainer ring 35 holds the shaft seal rings 32 in place with the
retainer ring 35 being held in place using a snap ring 41. A
sliding sleeve bearing 34 is installed within a recess 45 where the
shuttle assembly shaft 27 is installed along the shuttle assembly
support spindle 25 with two piston rings 47 sealing the shaft 27
from the operating chamber 30. A piston ring 43 surrounds the
operating flange 29 to travel along a liner sleeve 52 which retains
the operating seal 54.
[0060] A trigger valve air supply hole 61 is drilled through the
top wall of air passage 6 into the trigger valve air input chamber
63, enabling solenoid operated trigger valve 65 to be supplied with
air. When the trigger valve 65 is actuated by an electric pulse
from the firing circuit 42, a shot of air flows rapidly through
trigger air passage 58 into annular space 67 to trigger the air gun
by breaking the seal between the outside diameter of operating
flange 29 and operating seal 54 allowing the shuttle assembly to
start its firing movement as pushed by the air pressure within the
firing chamber 62 across the cross sectional area of the cup shaped
firing piston 30. Air vent passage 68 is drilled through bulkhead
wall 16 near the bottom of operating chamber 58 and air cushion
chamber 50, thus allowing the air pressure in the annular space 67
to be at ambient water pressure when the operating flange 29 has
returned to the set position. Check valve 69 positioned for outward
flow, vents water or air from ambient air cushion chamber 50
through drilled port 71. If any water seeps into the ambient air
cushion chamber 50 between air gun shots, the air is purged out
through check valve 69 by the temporary air pressure build up in
ambient air cushion chamber 50 during the time the cup shaped
firing piston 36 is moving from the set position as shown in FIGS.
1, 4A and 4B, to the right and back again, compressing the air from
about ambient water pressure and allowing some of the air to flow
through drilled passage 68 into ambient air cushion chamber 50 thus
pressurizing the chamber 50 and pushing any water which may have
collected in the bottom of the air cushion chamber 50 out through
check valve 69 and between the clearance of the cup shaped firing
piston rider bearing 179 and the cylindrical wall 20 of the housing
18. Recessed within the bulkhead wall 16, close fitting shaft seal
rings 32 and retainer ring 35 prevent air from the operating
chamber 30 from leaking through the center hole 11 of the bulkhead
wall 16 and the outside diameter of shuttle assembly shaft 27 when
the operating flange 29 is not in the set or cocked position.
[0061] When the air gun 10 is triggered, the liner sleeve 52 within
the operating chamber 30, as shown in FIG. 5A, controls the air
flow around the operating flange 29 to control the speed of the
operating flange 29 as described in patent, U.S. Pat. No. 4,779,245
to the same inventor. However, different from the described conical
tapered surface of revolution that would extend completely along
the inner surface 73 of the liner sleeve 52, the present invention
includes a series of non-contiguous flutes or grooves 75 shown in
FIGS. 5B and 5C as cross sections of the operating chamber 30 along
section A-A shown in FIG. 5A. The grooves 75 are machined into the
sleeve 52 and are formed as a shallow narrow groove at a first end
77, that expands to a deeper rounded channel along a middle area 79
and tapers to a less deep rounded channel 81 closer to the inner
wall 83 of the operating chamber head 26.
[0062] When the operating flange 129 is in the set to fire position
shown in FIG. 5A, there is none or very little air leakage around
the piston ring 43. When the trigger valve 65 is actuated by an
electric pulse from the firing circuit 42, the flange 129
accelerates from left to right. A time break transducer 44
installed at a passage from the operating chamber 130 transmits a
signal to the control circuit 42 that the air gun 10 has fired. As
shown in FIG. 5B, arrows indicate air flow as the piston ring 43 of
the flange 129 rides along the lands 73 of the inner surface of the
liner sleeve 52 between the grooves 75. The lands 73 guide the
piston ring 43 within the operating flange 129. By restricting air
flow initially through the formation of the shallow narrow shape of
the groove 75 at the first end 77, the rise time of the first
primary pressure pulse may be slowed until the operating flange 129
reaches the widened channel in the middle 79 of the groove 75. The
operating flange 129 then progressively accelerates until passing
the widened and deepened middle section when flange 129 nears the
end 81 where the slope and width of the grooves start to close off
the air flow, the flange 129 is slowed by compressing the air
within the operating chamber 130 to slow and stop the flange 129
prior to hitting the inner wall 83 of the operating chamber head
126. This is the point where the pressure peaks triggering the time
break transducer which puts out the signal that the gun has fired.
The speed of the operating flange 129 may therefore be controlled
by the geometry of the grooves where the shape, width, length,
slope and depth of the groove will all contribute to control of the
rise time of the primary pressure pulse. By slowing the rise time,
the time for the primary pressure pulse to reach peak pressure is
increased which may reduce some high frequencies that are
detrimental to marine life. Therefore, the appropriate groove
geometry at the lower operating pressures of the air gun 10 may
remove a source of spurious frequencies that may cause damage to
the hearing of marine mammals and fish.
[0063] In a further embodiment of the low pressure air gun 100, as
shown in FIG. 6, the solenoid valve housing 17 may be affixed to
the backbone 15 by vacuum oven brazing at mating surfaces 113
between the bottom of the housing 17 and backbone 15 thereby
eliminating the necessity of using bolts to attach the solenoid
valve housing 17. The operating chamber 130 is supplied with
compressed air directly from the air supply line 119 through inlet
131 and the hollow interior bore 153 of the shaft 127 is supplied
with air through inlet holes 137. The shuttle assembly shaft 127
extends through an opening in the operating chamber head 126. The
air cushion chamber 50 may be of a length L2 that is at least 1.2
times longer in length along the axis of the shuttle assembly as
measured in a set position from the inner face 76 of the firing
piston 36 to the inner surface 102 of the bulkhead wall 16 than the
length L1 within the operating chamber 30 along the axis of the
shuttle assembly as measured in a set position from the inner face
101 of the operating flange 129 to the inner surface 103 of the
operating chamber head 126. By increasing the length of the
distance from the inner face 76 of the cup shaped firing piston 36
to the bulkhead wall 16, there is less buildup of air pressure
within the air cushion chamber 50 when firing the air gun and
therefore the speed and travel distance of the cup shaped firing
piston 36 is less impeded. This provides for the discharge ports 70
to be opened more fully where the shuttle assembly is mostly slowed
and stopped by the air cushion build up within the operating
chamber 30. By opening the ports 70 more fully, the energy output
from operating the air gun 10 at lower pressures may be comparable
to high pressure air guns of the prior art. A fluid filled speed
controller 152 is affixed to the operating chamber head 126 using
bolts 124.
[0064] In this further embodiment which may be in addition to the
operating chamber speed controller 52, a hydraulic speed controller
152 may be installed to an extended portion of the shuttle assembly
shaft 127 of the air gun 100. The hydraulic speed controller 152 is
bolted using bolts 122 to the outside center of the firing chamber
head 126 of the air gun 100 to control the speed the shuttle
assembly travels after the air gun 100 is triggered. The hydraulic
speed controller 152 as shown in FIG. 7A includes an oil filled
chamber 154 with the shaft assembly 127 of uniform diameter
entering the opening 151 of the chamber 154 through two plastic
bearings 155 with a shaft seal 156 retained between the two
bearings 155. A check valve piston assembly 190 is installed to the
shaft 127 and a speed controller housing head 157 is bolted to the
top of the oil filled chamber 154 with an opening 158 for the end
of the shaft 127 to extend through the head 157. An internal shaft
seal 159 seals the outside diameter of the shaft 127 within the
speed controller head 157 and an O-ring seal 161 seals the head 157
to the housing 162. A threaded retainer cap 168 is inserted into
the hollow bore 153 to seal the shaft 127 and retain the check
valve piston assembly 190 that surrounds the shuttle assembly shaft
127. The check valve piston assembly 190 includes a piston 192 with
a ring of holes 194. The piston 192 is held in place within a bore
164 of the housing 162 by a tubular retainer 196 running through
the speed controller housing head 157 and shaft seal 159. There is
check valve plate 198 shaped like a circular washer biased against
the check valve piston 192 by a spring 202 to cover the piston
holes 194 causing the piston 192 with holes 194 and the spring
biased ring plate 198 to become a check valve to remain closed when
the shuttle assembly shaft 127 is accelerating upon triggering of
the air gun 100. A spring retainer 200 retains the spring 202 and a
ring plate 203 stops the spring biased ring plate 198 and sets the
distance that the spring biased ring plate 198 moves when the check
valve is opened. A cross sectional view of the speed controller 152
along section A-A of FIG. 7A is shown in FIG. 7B.
[0065] When the air gun shuttle assembly shaft 127 is in the set
position before triggering the check valve piston assembly 190 is
at the bottom of the speed controller housing 162 as shown in FIG.
7A where the clearance between the piston 192 and housing 162 is
small. After triggering the shuttle assembly shaft 127 moves a
short distance building pressure up in the housing 162 which acts
against the top of the piston 192 and check valve plate 198 closing
the holes 194 to retard and control the speed of the shuttle
assembly as shown in FIG. 7C. The piston 192 starts to move with
the shaft 127 over the outwardly tapered slope 163 of the housing
bore 164 and as the shuttle assembly moves a greater distance the
diameter around the piston 192 increases which allows the shuttle
assembly to move faster until a terminal velocity is reached by the
designed clearance between the piston 192 and housing 162. Thus the
speed of the shuttle assembly can be controlled by the length of
the bore and contour of the slope of the speed controller housing
162. After the shuttle assembly halts its movement after firing it
reverses itself to return to the set position and during the return
stroke the check valve plate 192 of the hydraulic piston assembly
190 opens to allow free hydraulic fluid such as oil to flow so that
the shuttle assembly can return freely to its set position. By
controlling the speed of the shuttle assembly shaft 127 through the
geometry of the hydraulic speed controller bore 164 and slope 163
of the housing 162 the rate of rise of the outgoing sound pulse of
the air gun may be adjusted to control the frequency content of the
outgoing pulse in order to eliminate undesired high frequencies
from the pulse.
[0066] As shown in FIG. 8A, due to the very rapid acceleration of
the shuttle assembly of high pressure air guns, a very sharp sound
output spike occurs when the end surface 172 of the opening cup
shaped firing piston 36 clears the opening edge 165 of the exhaust
ports 70. The rapid rise time of the resulting sound spike is so
sharp, it may produce an abundance of high frequency sound in the
surrounding water which is thought to be damaging to marine life
such as fish and marine mammals. In order to reduce these spurious
high frequencies in a low pressure air gun, a sliding firing seal
167 is installed on the outer diameter of the cup shaped shuttle
assembly flange 36 to prevent the leakage of air prior to the end
surface 172 of the cup 36 clearing the edge 165 of the port. The
sliding firing seal 167, as shown in FIG. 8B is held securely
between the contoured spring loaded back ring 169 and contoured
shoulder 173 of the housing 18. A spring 171 is positioned within
the spring loaded back ring 169 to provide the force to hold the
firing seal 169 against the shoulder 173. In the set position the
sliding firing seal 167 seals the outside diameter of the cup
shaped firing piston 36 to retain the air within the firing chamber
62. A seal 177 seals the inside diameter of the spring loaded
backup ring 169. The firing piston 36 rider bearing 179 is
installed around the outer diameter of the upper portion of the cup
shaped firing piston 36.
[0067] In an embodiment of the present invention, the width of the
ports W extends beyond the outer diameter OD of the cup shaped
firing piston 36 providing for as much air as possible to be
expelled from the firing chamber with the shortest distance travel
of the shuttle assembly shaft 27 improving the overall efficiency
of the low pressure air sun 10. The ports 70 are formed as divider
ports with strengthening horizontal posts 180 to give the air gun
housing 18 rigidity between each of four ports shown in FIG. 8C in
cross section of section A-A shown in FIG. 8A.
[0068] In operation at pressures lower than 1000 psi, the shuttle
assembly shaft 27 accelerates when the air gun 10 is triggered and
the bottom outside diameter surface 163 of the cup shaped firing
piston 36 moves until it passes the sealing surface of the sliding
firing seal 167. The spring loaded backup ring 169 maintains a
force on the sliding firing seal 167 to prevent any leakage from
around the outer diameter of the cup shaped firing piston 36.
Therefore, while moving toward the edge of the ports 165 within the
air gun housing 18 no compressed air is released from the
compression chamber 30 during the acceleration distance. The
reduction of air leakage and lower velocity of air as it
accelerates out of the ports 70 at lower pressures reduces the
content of high frequencies in the outgoing pulse and differently
from conventional high pressure air guns, may reduce cavitations in
the water that may disrupt the marine ecostructure and with the
objectionable high frequencies may damage the hearing of marine
mammals.
[0069] Although specific embodiments of the invention have been
disclosed herein in detail, it is to be understood that this is for
purposes of illustration. This disclosure is not to be construed as
limiting the scope of the invention, since the described
embodiments may be changed in details as will become apparent to
those skilled in the art in order to adapt the low pressure air
guns to particular applications, without departing from the scope
of the following claims and equivalents of the claimed
elements.
* * * * *